Cable stranding is a process in which individual wires are combined, typically in a helical arrangement, to produce a finished cable. See, e.g., U.S. Pat. Nos. 5,171,942 and 5,554,826. The resulting stranded cable or wire rope provides far greater flexibility than would be available from a solid rod of equivalent cross sectional area. The stranded arrangement is also beneficial because a helically stranded cable maintains its overall round cross-sectional shape when the cable is subject to bending in handling, installation and use. Such helically stranded cables are used in a variety of applications such as hoist cables, aircraft cables, and power transmission cables.
Helically stranded cables are typically produced from ductile metals such as steel, aluminum, or copper. In some cases, such as bare overhead electrical power transmission cables, a helically stranded wire core is surrounded by a wire conductor layer. The helically stranded wire core could comprise ductile metal wires made from a first material such as steel, for example, and the outer power conducting layer could comprise ductile metal wires made from another material such as aluminum, for example. In some cases, the helically stranded wire core may be a pre-stranded cable used as an input material to the manufacture of a larger diameter electrical power transmission cable. Helically stranded cables generally may comprise as few as seven individual wires to more common constructions containing 50 or more wires.
FIG. 1A illustrates an exemplary helically stranded electrical power transmission cable as described in U.S. Pat. No. 5,554,826. The illustrated helically stranded electrical power transmission cable 20 includes a center ductile metal conductor wire 1, a first layer 13 of ductile metal conductor wires 3 (six wires are shown) stranded around the center ductile metal conductor wire 1 in a first lay direction (clockwise is shown, corresponding to a right hand lay direction), a second layer 15 of ductile metal conductor wires 5 stranded around the first layer 13 in a second lay direction opposite to the first lay direction (counter-clockwise is shown, corresponding to a left hand lay direction), and a third layer 17 of ductile metal conductor wires 7 stranded around the second layer 15 in a third lay direction opposite to the second lay direction (clockwise is shown, corresponding to a right hand lay direction).
During the cable stranding process, ductile metal wires are subjected to stresses beyond the yield stress of the metal material but below the ultimate or failure stress. This stress acts to plastically deform the metal wire as it is helically wound about the relatively small radius of the preceding wire layer or center wire. There have been recently introduced useful cable articles from materials that are composite and thus cannot readily be plastically deformed to a new shape. Common examples of these materials include fiber reinforced composites which are attractive due to their improved mechanical properties relative to metals but are primarily elastic in their stress strain response. Composite cables containing fiber reinforced polymer wires are known in the art, as are composite cables containing ceramic fiber reinforced metal wires, see, e.g., U.S. Pat. Nos. 6,559,385 and 7,093,416; and Published PCT Application WO 97/00976.
One use of stranded composite cables (e.g., cables containing polymer matrix composite or metal matrix composite wires) is as a reinforcing member in bare electrical power transmission cables. Although electrical power transmission cables including aluminum matrix composite wires are known, for some applications there is a continuing desire to obtain improved properties. The art continually searches for improved stranded composite cables, and for improved methods of making and using stranded composite cables.